EEG and Evoked Potentials in the Diagnosis of Dementias

Abstract

The EEG in normal adults is characterized by an occipitally dominant 10-Hz alpha rhythm (Fig. 1). The alpha rhythm is reactive, meaning it is attenuated when the eyes are open (Fig. 2) and reappears after eye closure. Even centenarians may have an EEG with a normal alpha rhythm. However, Busse et al. (1956) found that 51% of normal subjects over 60 years of age showed slight EEG abnormalities, mainly focal, in the anterior-temporal regions. The percentage of focal abnormalities increases with age from about 20% in the 40–59-year-old to about 30%–40% in the 60–79-year-old group (Busse and Obrist 1965). These findings have been confirmed by several other authors. The proportion of focal changes in normal aged subjects should not exceed 25% of the EEG record.